Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 311123
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
323 AM PST Sat Jan 31 2015
Light precipitation possible in far northern portions late Sunday
into Wednesday. Some breezy north to east wind continues into
Saturday with above normal temperatures. Night and morning fog
possible in the Central Valley Sunday into early next week.
Models suggest change to a potentially wet weather pattern towards
the end of next week.
.Short Term Discussion (Today through Tuesday)...
Positive-tilt upper ridging continues to build over NorCal today
as upper low to the south digs southeastward. The N-S low level
pressure gradient becomes more E-W dominated today. This will
favor stronger winds over the eastern foothills/mountains and
along the west side of the Sacramento Valley into the Delta.
The airmass undergoes synoptic warming today with increasing
heights/thicknesses. Highs tomorrow approach near records in the
Sacramento Valley with readings in the low to mid 70s. Yesterday
Sacramento Executive Airport tied a record of 69F, set in 1976.
Upper ridging flattens some Sunday as impulses ride over the top of
it into the PacNW. Greater area of morning valley fog possible in
the San Joaquin and possibly into the Southern Sacramento Valley and
Delta Sunday under lighter surface wind and increased subsidence.
Some associated overrunning cloudiness Sunday and Monday will
result in slight cooling over Interior NorCal. Models depict
potential for some light overrunning precip over mainly
Shasta/Plumas/Tehama counties Sunday night into Tuesday.
.Extended Discussion (Wednesday through Saturday)
Upper ridge centered along the west coast at mid-week is forecast
to shift into the Rockies by the end of the week setting up a
period of moist southwesterly flow across the area late in the
week. Relative measure of predictability of the large-scale
features (ridge over the Rockies and trough over the Gulf of
Alaska) is high, so confidence in the pattern developing toward
wet late next week is continuing to increase.
Models depict a wide swath of deep TPW (in excess of 1.5 inches)
extending into NorCal late in the week with increasingly strong
forcing coming into play by Friday. At this time, appears the
heaviest QPF is still centered mainly north of I-80 by the GFS.
We`ll continue to monitor trends.
Mainly VFR conditions across interior NorCal next 24 hours,
except local MVFR/IFR conditions in the Northern San Joaquin
Valley early this morning.
North winds 10-20 kt along the northern and western Sacramento
Valley will continue through midday, then diminish. Over higher
terrain, areas 25-35 kts decreasing this afternoon.